Mixing of various materials, for example paint, has heretofore been affected by manually mixing or agitating the material, such as by stirring or shaking. For example, U.S. Pat. No. 3,894,723 is directed to a mechanical agitator, while U.S. Pat. Nos. 1,908,561 and 3,265,366 disclose paint shaking devices. The mixing action is relatively slow and inefficient in these devices. Material shaking devices, such as paint shakers, require substantial mechanical structure and a heavy base or anchoring since vibration is a major problem. Due to vibration and the force of the material on the lid of the container, a cumbersome clamping apparatus must be employed to tightly retain the lid in position during the shaking operation. U.S. Pat. Nos. 2,599,833 and 2,894,309 disclose clamping apparatuses for use with containers in shaking devices.
Others achieve mixing by accelerating material in a container first in one direction and then in a second opposite direction to achieve mixing by the combination of shear forces and the creation and destruction of a vortex in the material. A mixer of this type is shown in U.S. Pat. No. 3,542,344. While a mixer of this type reduces the problems of vibration and eliminates the necessity to clamp the lid on the container, substantial power and braking apparatus are required to effect the acceleration and reversal of the material in the container.
Another type of mixer spins the container in one direction and oscillates the container at the same time. An example of this type of device is disclosed in U.S. Pat. No. 3,181,841. This type of device also requires a complicated mechanical structure, disadvantageously causes vibration and requires clamping of the lid or cover of the container.
Still another type of mixing apparatus simultaneously spins a container of material about two perpendicular axes, or gyroscopically. U.S. Pat. No. 3,880,408 discloses a device in which the container is rotated continuously about the two axes, whereas U.S. Pat. No. 3,706,443 discloses apparatus which rotates the container continuously about one axis but only rocks about a second, perpendicular axis by gyroscopic forces due to imbalance in the system. While the resulting mixing action is relatively rapid, a complicated mechanical structure is required and, because of the vibration, the lid must be securely clamped to the container.
Another type of gyroscopic mixer which has become a standard in the paint industry is disclosed in U.S. Pat. No. 4,235,553. The mixer simultaneously rotates the fluid container in one direction about a first axis and simultaneously rotates the container about a second axis which is non-perpendicular to the first axis. The rotation of the container about two different, non-perpendicular axes results in efficient bottom circulation of the fluid material within the container.
At least two problems associated with the gyroscopic-type mixers disclosed in the '408, '443 and '553 patents relate to the drive mechanisms and the supporting structure for holding the fluid container. First, the supporting structures are typically fixed in size and unable to accommodate containers that are smaller or larger than the standard cylindrically-shaped paint can. A second problem associated with these devices lies in the drive mechanism. Specifically, the complicated belt arrangement is typically required between the supporting structure that holds the fluid container and the motor. The belts are prone to wear and are difficult to replace.
Accordingly, there is a need for an improved mixer for fluid materials and suspensions which is capable of accommodating containers of different and varying sizes and shapes and which provides the benefits of gyroscopic mixing but with an improved, more efficient and simplified drive mechanism.